[llvm] [Github] Add Pull Request template with links to Github docs/Discord/Forums (PR #71923)

[Tobias Hieta via llvm-commits]

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@@ -0,0 +1,10 @@
+<!-- THIS COMMENT IS NOT VISIBLE IN THE FINAL PR, BUT FEEL FREE TO REMOVE IT.
+Thankyou for submitting a Pull Request (PR) to the LLVM Project!
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tru wrote:

missing space here

https://github.com/llvm/llvm-project/pull/71923